New genetic technologies, combined with a well-characterized genome, make the mouse the preferred mammalian model for human disease. The generation and characterization of mouse strains harboring genetically predetermined pathobiological syndromes is critical to biomedical research, and researchers at the Jackson Laboratory (TJL) are at the forefront of this endeavor. Full exploitation of mouse models rely on access to critical technologies. Over 35% of TJL's research staff rely heavily on flow cytometric techniques to carry out studies in the areas of immunology, diabetes, hemopoietic stem cell biology, gene therapy and cancer research. Flow cytometry constitutes an essential tool for quantitative multiparameter measurements of membrane and internal proteins on individual cells, for gene expression analysis and cell cycle regulation. TJL's current flow cytometry instrumentation is overburdened and it is becoming too outmoded to meet the demands of our NIH funded research projects. The basic data collection limitations make it more costly to carryout multiparameter analyses and thus limit the application of emerging flow technologies necessary to remain competitive. The Becton-Dickinson FACSCalibur Flow Cytometry System has proven its reliability in both clinical and research settings. Because of its automated sample loader, flexible and efficient sorting capability and user friendly interface, the FACSCalibur is a cost-efficient solution enabling investigators to maximize the potential of their mouse models. Funds are requested to purchase the FACSCalibur Flow Cytometry System, to be operated by the institution's Flow Cytometry Service thus providing a cost-effective way to fill an urgent and unmet need of TJL Staff.